Adaptive Input-Power Distribution in Doherty Power Amplifiers for Linearity and Efficiency Enhancement

A new technique based on an adaptive input-power distribution is introduced to overcome the limitations of practical Doherty power amplifiers. The proposed Doherty amplifier employs an extended-resonance power-divider at its input. By taking advantage of the auxiliary cell´s nonlinear input impedance, the extended-resonance divider is designed such that it provides a proper power-dependent power-division between the main and auxiliary cells. Therefore, the two cells are efficiently driven and can generate output current and voltage characteristics similar to the ideal Doherty amplifier, resulting in both linearity and efficiency improvements. The performance of the new Doherty amplifier is compared with a conventional design through simulations and measurements. The proposed Doherty amplifier achieves a measured ACLR improvement of 5-7 dB over a wide range of output power levels, as well as an increased power-added-efficiency of up to 5% for WCDMA signals. The proposed Doherty design does not require complex circuitry and yields a compact circuit.